The present application claims priority to Japanese Application No. P2000-102413 filed Apr. 4, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to an antireflection filter for a display device.
2. Description of the Related Art
When a viewer watches something through a transparent material such as glass, reflected light on the glass surface is strong so that, if a reflected image is clear, then a viewer will be troubled.
For example, a reflected image such as so-called ghost and flare is produced on lenses for glasses and a viewer will be troubled.
Furthermore, it is frequently observed that a user cannot clearly see contents through a looking-glass or the like due to light reflected on the glass surface.
When a problem that a sense of sight is troubled by reflected light is solved, in order to prevent reflection, heretofore, there has been proposed a method in which an antireflection layer is formed by coating a material having a different refractive index on a base material by vacuum deposition or the like.
In this method, there is known that an antireflection effect can be increased by properly setting a thickness of an antireflection layer formed on the base material.
For example, when this antireflection layer is formed as a single layer structure, in order to minimize a reflectance or to maximize a transmittance, it is effective to use a material having a lower refractive index than a base material of an underlayer and to select an optical film thickness to be xc2xc of wavelength of light or to be odd-numbered times of xc2xc.
Here, the optical film thickness is given by the product of the refractive index of the material for forming a coated film and a film thickness of the coated film.
It is proposed that an antireflection layer is formed as a multilayer structure. In this case, there are various proposals with respect to selection of a film thickness of an antireflection layer (OPTICAL TECHNOLOGY Vol. No. 8, p17 (1971)).
On the other hand, Japanese laid-open patent application No. 58-46301 and Japanese laid-open patent application No. 59-49501 have proposed methods in which a multilayer structure antireflection layer which can satisfy a condition of the above optical film thickness by using liquid composition.
In recent years, there are proposed optical products having antireflection property in which plastics material is used as a base material by effectively utilizing good points in which plastics material is light in weight, safe and is easy to handle. These optical products have been put into practice. Most of the optical products have an antireflection layer made of a material containing silicon dioxide formed on the surface.
However, when the antireflection layer is deposited on the above base material by vacuum deposition, as the material of this antireflection layer, there are mainly used inorganic oxide or inorganic halogenide.
When glass is used as the base material, there arises a problem that, although the antireflection layer of the upper layer has high surface hardness, when it is smudged by user""s finger marks, finger prints, sweat, liquid hair tonic, hair spray or the like, smudges are conspicuous and these smudges are difficult to be removed.
Since such antireflection layer is poor in surface smoothness, it is easy to be scratched conspicuously. Further, since such antireflection layer has large wetting against water, when it is smudged by raindrops or splashes of other water, large marks are easily left on the surface of the antireflection layer. In particular, there arises a problem that, when a user watches an object through glasses, the object is distorted over a large area.
In the antireflection layers described in the above Japanese laid-open patent application No. 58-46301, the above Japanese laid-open patent application No. 59-49501 and Japanese laid-open patent application No. 59-50401, there are described technologies in which the uppermost layer contains more than 30 [parts by weight] of inorganic material represented by silica fine-grained particles provide a high surface hardness. The antireflection layer obtained by the above composition encounters with a problem that it becomes poor in surface smoothness, it is easy to be scratched by friction of clothes or the like and its scratches become conspicuous.
In order to improve the above problems, there are proposed and appear on the market various surface finishing agents.
However, since any these surface finishing agents are dissolved by water and various solvents, even when the surface of the antireflection layer is treated by the surface finishing agent, the surface finishing effect is not lasting and is therefore poor in durability.
Japanese laid-open patent application No. 3-266801 has proposed a technology in which a fluororesin layer is formed to provide water repellent property. However, although the water repellent property can be provided by using the fluororesin, satisfactory results of durability with respect to friction and abrasion on the surface could not be obtained yet.
In order to improve durability with respect to friction and abrasion on the surface and to solve a problem of pollution resistance, there is proposed a technology in which an antireflection layer is surface-finished by perfluoropolyether compound (Japanese patent application No. 7-224063).
However, in the technology proposed by the above Japanese patent application No. 7-224063, since a chemical stability of surface finishing agent is not satisfactory, there arises a problem that antireflection effect of the surface is considerably deteriorated by a treatment with a solvent or the like
Japanese laid-open patent application No. 9-61605 has proposed a technology in which a problem of wear and abrasion resistance or pollution resistance of a display device filter having antireflection property can be solved by coating the surface with alkoxysilane compound having perfluoropolyether group.
In the technology proposed in the Japanese laid-open patent application No. 9-61605, in order to enable SiO2 component in the glass of the underlayer of the antireflection layer and a material used to form the antireflection layer to interact with each other, a strong linkage with the SiO2 component can be formed by causing molecular structure to contain alkoxysilane group.
However, in the antireflection layer proposed in this Japanese laid-open patent application No. 9-61605, having considered this antireflection layer from a wear and abrasion resistance standpoint, it is to be understood that this antireflection layer has rooms to be improved in characteristic.
Specifically, in the antireflection layer proposed in the Japanese laid-open patent application No. 9-61605, since the alkoxysilane compound chemically reacts with the SiO2 component, the surface of this material has no migration. Consequently, when friction contact occurs in actual practice, if this material is removed from the portion in which the friction contact occurred, then such damaged portion will not be restored by movement of materials from its periphery.
Accordingly, after earnest researches, the assignee of the present application proposes an antireflection filter for display device in which the above problems can be solved.